The present invention pertains primarily to flywheels, and more particularly to flywheels for use with an automotive engine or the like.
Generally, the starting mechanism for an internal combustion engine such as an automotive engine comprises an electric starting motor which is engaged via a pinion gear to mating teeth on a flywheel, which in turn is attached to the crankshaft of the engine. When the electric starting motor receives electric current from an electric storage battery, the teeth of the pinion gear on the end of the motor armature shaft are automatically brought into engagement with the teeth of the flywheel, thereby causing the crankshaft to rotate. Once the engine has started, that is, once the engine commences operation via the typical internal combustion cycle, the pinion gear of the starting motor is automatically disengaged, and the flywheel continues to rotate due to the movement of the crankshaft.
There are two different types of flywheels used with automotive engines or the like. The first type is used with a manual transmission and usually comprises a massive cast metal assembly, which in addition to providing mounting means for the bell housing and clutch of the transmission, more importantly provides inertia in the classic flywheel sense to keep the engine from stalling out. This type of casting usually has a ring gear shrunk or sweated on to its outer circumference. The teeth on the ring gear engage the teeth on the starting motor pinion gear. The second type of flywheel is used with an automatic transmission and usually comprises a relatively thin metal stamping, called a flexplate, having a ring gear attached, usually by welding, to the outer circumference thereof. Although this type of flywheel is not really used to provide any inertia for the engine, a torque converter is usually mounted thereon as part of the transmission. The present invention relates primarily to this second type of flywheel, although it is contemplated that the basic idea of this invention might also be applied to the first type of flywheel described above with appropriate modifications. The term "flywheel" is used herein as including said second type.
A typical flywheel for use with an automatic transmission would in part be comprised of a stamping made from material such as S.A.E. 1010 hot rolled aluminum killed steel having a Rockwell "B" hardness of between about 55 and 75. The stamping could be made in either a progressive or transfer die system, washed, and then shot peened to provide additional strength. The resulting stamping would be disc-shaped and have holes appropriately placed therein for mounting and aligning the crankshaft of the engine, the torque converter, and the transmission. A small disc-shaped wear plate may have to be welded on to the hub area of the flexplate where the flexplate is mounted on the crankshaft. The outer edges of the flywheel would be bent 90.degree. to provide an attaching surface or flange for the ring gear which is welded thereto.
The ring gear is typically made from such material as S.A.E. 1040/1050 fine grain steel. It is usually manufactured by cutting a strip from a long bar; wrapping it in a circle; buttwelding the ends together; reforming, rounding, and flattening the piece; machining the inner diameter; machining and chamfering the top face; machining and chamfering the lower face; cutting the gear teeth on the outer diameter; and then heat treating the piece. The ring gear is then usually welded to the stamped disc or flexplate described above. Weld slag is removed from the resulting flywheel assembly and then it is balanced.
Although the typical two-piece flywheel described above for use with automatic transmissions is widely used, it does possess several disadvantages. For example, it should be readily apparent from the above description that the flywheel assembly is rather complicated to manufacture, that is, both of the parts in the two-piece assembly require several manufacturing steps. Inherent in the design and construction of this two-piece flywheel are such problems as: (1) lack of concentricity and teeth run-out, in which the ring gear is not perfectly matched to the circumference of the inner flexplate and in which the gear teeth therefore vary in radial distance from the crankshaft; and (2) face wobble, in which the respective planes of the flexplate and ring gear are different rather than the same.
Accordingly, it is a principle object of the present invention to provide a flywheel for use with an automotive engine or the like which may be fabricated in one piece and then selectively reinforced where necessary, thereby eliminating the need for attaching a separate ring gear to a flexplate or stamped metal disc.
In general, the flywheel according to the present invention is a one-piece construction which comprises a generally flat, disc portion having a hub and aperture in the center thereof for mounting and alignment on the crankshaft of the automotive engine or the like, and a ring portion integrally formed with and positioned around the outer circumference of said disc portion. The ring portion has radially-outwardly extending teeth thereon adapted to engage mating teeth on the engine's starting motor pinion gear. A separate and distinct reinforcement segment or member is applied in overlapping relationship on the teeth of the ring portion to provide additional strength to the teeth at the points where the starting motor pinion gear is initially engaged.
With regard to a typical automotive four-cylinder engine, and by way of illustration of the present invention, it has been found that only two discrete reinforcement segments are necessary on the teeth of the ring portion. This is because a typical automotive four-cylinder engine always stops at one of two possible locations in a 360.degree. rotation due to the relative locations of the pistons in the engine and the balancing of compression forces when the engine is turned off. (The only known exception to this is what is known as a "false start", in which an attempt is made to "start" the engine when it is already running, thereby causing the starting motor pinion gear to strike a rotating flywheel rather than one that is normally stationary before engagement.) Normally, therefore, the reinforcement segments are only necessary at two points on the flywheel, these two points being the only two locations where the pinion gear of the starting motor engages the teeth on the ring portion of the stationary flywheel. These two locations must bear the brunt of the forces exerted by the pinion gear against the flywheel. Since a six-cylinder engine stops in three different locations and an eight-cylinder engine stops in four different locations, it is contemplated that the present invention is equally applicable in those situations by using three and four reinforcement segments respectively.
Additional advantages and features of the present invention will become apparent from a reading of the detailed description of the preferred embodiment which makes reference to the following set of drawings in which :